This section is intended to introduce various aspects of the art, which may be associated with exemplary embodiments of the present techniques. This discussion is believed to assist in providing a framework to facilitate a better understanding of particular aspects of the present techniques. Accordingly, it should be understood that this section should be read in this light, and not necessarily as admissions of prior art.
Since the 1970s, flexible pipes have been utilized in the hydrocarbon industry as flow lines, risers, and jumpers, among others, to transport raw materials, production fluids, and other materials associated with offshore oil and gas production. Overall, the enhanced flexibility and versatility of a flexible pipe lends to a more economical design solution for transporting offshore oil and gas. In particular, the flexible pipe has an advantage over a rigid pipe of the same diameter due to its relatively low ratio of bending to axial stiffness.
The structure of the flexible pipe typically includes a number of layers of different materials in the pipe wall fabrication. One such layer may include a metal layer, or an inner carcass, that is permeable to production fluids and is in direct contact with such fluids. The function of the inner carcass is to prevent the collapse of the flexible pipe as a result of gas expansion or hydrostatic pressure of sea water. Another layer of the flexible pipe may include a polymer sheath that can be used as an inner sheath layer and an outer sheath layer. The inner sheath layer may be implemented to maintain the integrity of the production fluids. Thus, the type of materials selected for the inner sheath layer may be based on various parameters, such as the inner production fluid temperature, composition, and pressure. The outer sheath layer may be implemented to provide a barrier against factors external to the flexible pipe, including seawater diffusion and mechanical damage.
The flexible pipe may include an annular region located between the inner sheath layer and the outer sheath layer. The annular region may comprise armor layers that can include one or more pressure armor layers and tensile armor layers. Accordingly, pressure armor layers may be implemented to withstand internal pressure exerted by the inner production fluids. Tensile armor layers may be implemented to resist the tensile load on the flexible pipe. For example, the tensile armor layers may be utilized to support the weight of the flexible pipe as it extends from a side of a vessel and to transfer the load of the flexible pipe to the vessel and into a seabed.
The armor layers within the annular region may typically include a high strength material. Yet, the possibility for the diffusion of acid gases from the production fluids through a breached inner sheath layer may create a corrosive environment within the annular region, e.g., initiating corrosion or other degradation of the armor layers within the annular region. Further, there is a possibility that condensation or accidental damages to the outer sheath layer may result in the infiltration of water into the annular region, thus, leading to corrosion or other degradation of the armor layers. The resulting corrosion or other degradation of the armor layers in the annular region may affect production operations, which may shorten the lifespan of the flexible pipe and interfere in production operations, among other effects.
As one particular example, cathodic protection may be used to inhibit corrosion in the annular region. However, cathodic protection may be ineffective in preventing corrosion of the armor layers over the expected lifespan of the flexible pipe. Additionally, the use of traditional corrosion inhibitors may present challenges. For example, it may be difficult to supply a corrosion inhibitor to the annular region to protect the armor layers from corrosion or other degradation. Moreover, such corrosion inhibitors may accelerate the aging of the sheath layers, for example, by degrading the plastic that may make up the sheath layers.
U.S. Patent Application Publication No. 2013/0032240 A1 by Kuhmann, et al., describes a flexible pipe with a multilayer structure and unbonded layers. The flexible pipe has an interior lining that includes several layers. One of the layers may include materials selected from a group including polyolefin-molding composition, polyamide molding composition, and polyvinylidene fluoride molding composition. Another layer may include at least one layer of material that is composed of a molding composition based on a polymer selected from a group including polyarylene ether ketone, polyphenylene sulphide, polyarylene ether ketone/polyphenylene sulphide blend, polyphenyl sulphone, and polyalkylene naphthalate. The exterior reinforcement of the flexible pipe may provide protection from corrosion due to its constituents, which diffuse outwards from the fluid conveyed.
International Patent Application Publication No. WO 2012/006998 A1 by Glejbøl describes an unbonded flexible pipe with a length and a center axis along its length. The unbonded flexible pipe includes an internal sealing sheath surrounding the center axis and at least two tensile armor layers comprising cross wound elements surrounding the internal sealing sheath. The two tensile armor layers include a first tensile armoring layer including a plurality of first helically wound, elongate armoring elements and a second tensile armoring layer including a plurality of second helically wound, elongate armoring elements. The first helically wound, elongate armoring elements include a first material or a first combination of materials and the second helically wound, elongate armoring elements include a second material or a second combination of materials, where the first material or the first combination of materials is different from the second material or the second combination of materials. The unbonded flexible pipe further comprises a galvanic barrier between the first and the second tensile armoring layers. The galvanic barrier may consist of a peroxide containing polyolefin.
The aforementioned devices and techniques may facilitate the use of a flexible pipe in some applications. However, flexible pipes are often avoided for production fluids with a high acid gas content, e.g., greater than about 5% total content. Thus, there remains an ongoing need for more efficient techniques to inhibit or eliminate corrosion and other degradation of armor layers within the flexible pipe.